Going up–going down: How good are people at forecasting trends and changes in trends?

Prior studies of judgemental time-series forecasting have found that people have problems with downward-sloping series. This laboratory-based study presents a controlled experiment of series direction and it investigates the problems of changing trends. Results confirm that people have significant difficulties in dealing with downward-sloping series and that behaviour is consistent with a general tendency to anticipate that downward series will reverse themselves. There is a significantly less tendency to do so for upward series. Results are discussed in terms of systematic and unsystematic error.